Laser printers typically offer a greater improvement in resolution over dot matrix and ink jet-type printers, and the trend is to offer ever greater resolution in dots per inch (dpi), and to increase the throughput of pages printed per minute (PPM). In most cases, a particular family of conventional printers manufactured by a given manufacturer would always contain the same laser scanning unit (referred to as a "printhead"), and since there was only one type of available printhead, the print engine programming code (e.g., software or firmware) always assumed the correct printhead was installed in the printer. However, to reduce cost and reliance on a single vendor of printheads, it would be possible to make a laser printer compatible with more than one particular printhead model, although it would be very important to know which model printhead was actually installed within the printer.
Some conventional printers use an identification circuit on their printheads, such as in U.S. Pat. No. 5,363,134 (by Barbehenn). The printhead of an ink jet printer is disclosed as including an identification circuit on the same substrate as the jet array circuit. The identification circuit includes programmable pads that each include an active device (such as a diode or transistor) and programmable fuses. The identification circuit provides information about which type of ink jet cartridge has been installed, including information such as which color ink is included in this cartridge.
Another patent, U.S. Pat. No. 4,872,027 (by Buskirk), discloses a printhead used in a dotmatrix printer, in which the printhead includes extra pathways that can be connected to different resistors to provide a "code." The printer reads the code and can be automatically reconfigured accordingly, because the code represents the type of color of the printhead. Buskirk also discloses other means of identification of a printhead, such as the use of a projection or depression in the printhead that can be sensed by a limit switch, the use of a bar code reader, or some other type of optical reader that detects reflecting areas on the printhead.
U.S. Pat. No. 5,049,898 (by Arthur) discloses an ink jet printer in which the printhead includes a memory element that can be read by the printer. This memory element contains data used to identify the printhead, and can be used to identify the color of the printhead's ink, or some other parameter. Similarly, U.S. Pat. No. 5,504,590 (by Kawada) discloses a copier that can detect whether or not a correct operational panel is installed. A "code" is sent to a remote processing unit which provides information as to the type of display or other parameters of the operator panel. If an incorrect display is discovered by the processing unit, a message is provided on the display to warn the user that the operational panel should be changed.
U.S. Pat. No. 5,491,540 (by Hirst) discloses a printer or copier having a serial interface between the printer/copier and certain replacement parts. The interface allows information about use, calibration, or other parameters to pass to the replacement part from the printer, after the new part has been installed.
U.S. Pat. No. 5,868,673 (by Negoro) discloses a laser beam scanner with a regulator that keeps the scanning speed of the beams uniform in the "target" region. The scanning speed is controlled so as to produce a more precise printer, and this is accomplished by using a photo-sensor drum that is used to detect the rotational speed of a polygonal scanner that is mounted to the drive motor. Negoro assumes that the correct printhead or print engine has already been installed.
While conventional printers assume that the printhead that has been installed is of a certain known type, greater flexibility could be achieved by making the printer compatible with more than one style printhead. It would be beneficial to be able to detect whether or not the correct laser scanning unit or printhead has been installed into the laser printer without having to rely on additional sensors or other hardware that would both add complexity to the printer and add cost to manufacture.